Image sensing device and operating method thereof

1. An image sensing device comprising: a charge sensing circuit configured to generate first charges, which correspond to incident light, based on a photo control signal; a reset circuit configured to reset the charge sensing circuit based on a reset signal; a floating diffusion node configured to accumulate the first charges; a compensation circuit configured to selectively couple the floating diffusion node to a global bias line based on a compensation control signal and selectively supply a compensation current to the floating diffusion node based on the compensation control signal; and a selection circuit configured to output a pixel signal, which corresponds to a voltage on the floating diffusion node, to a readout line based on a selection signal.

2. The image sensing device of claim 1 , wherein the compensation control signal indicates whether the floating diffusion node is saturated.

3. The image sensing device of claim 1 , further comprising: a signal converting circuit configured to convert the pixel signal, as an analog signal, into a digital pixel signal; and a compensation control circuit configured to generate the compensation control signal based on the digital pixel signal.

4. The image sensing device of claim 3 , wherein the compensation control circuit generates the compensation control signal for compensating for a pixel signal to be generated during a current frame period, based on the digital pixel signal generated during a previous frame period.

5. The image sensing device of claim 3 , wherein the compensation control circuit includes: a comparator configured to compare the digital pixel signal with a reference signal; a memory configured to store a comparison signal outputted from the comparator, and generate first and second selection information signals corresponding to the comparison signal; a first buffer configured to buffer the first selection information signal, and generate the compensation control signal; a second buffer configured to buffer the second selection information signal, and generate a selection control signal; and a bias controller configured to generate a bias control signal.

6. The image sensing device of claim 5 , further comprising: a bias current generating circuit configured to supply a bias current, which corresponds to the compensation current, to the compensation circuit based on the bias control signal and the selection control signal.

7. The image sensing device of claim 6 , wherein the bias current generating circuit includes: a current source circuit configured to generate the bias current based on the bias control signal; and a switch configured to selectively couple the current source to the compensation circuit based on the selection control signal.

8. The image sensing device of claim 3 , wherein the charge sensing circuit, the floating diffusion node, the compensation circuit and the selection circuit are disposed in an analog region, and wherein the compensation control circuit is disposed in a digital region.

9. An image sensing device comprising: at least one pixel configured to generate an analog pixel signal, which corresponds to reflected light that remains after background light of incident light is removed, based on a compensation control signal, the reflected light being reflected from a subject; a signal converting circuit configured to convert the analog pixel signal into a digital pixel signal; and a compensation control circuit configured to compare the digital pixel signal with a reference signal, store a comparison signal corresponding to the comparison result, and generate the compensation control signal corresponding to the comparison signal.

10. The image sensing device of claim 9 , wherein the pixel includes: a charge sensing circuit configured to generate first charges, which correspond to the incident light, based on a photo control signal; a floating diffusion node configured to accumulate the first charges; a compensation circuit configured to supply selectively a compensation current, which corresponds to the background light, to the floating diffusion node based on a compensation control signal; and a selection circuit configured to output a pixel signal, which corresponds to a voltage on the floating diffusion node, to a readout line based on a selection signal.

11. The image sensing device of claim 10 , wherein the compensation control signal indicates whether the floating diffusion node in the pixel is saturated.

12. The image sensing device of claim 9 , wherein the compensation control circuit compensates for a pixel signal to be generated during a current frame period, based on the digital pixel signal generated during a previous frame period.

13. The image sensing device of claim 9 , wherein the compensation control circuit includes: a comparator configured to compare the digital pixel signal with the reference signal; a memory circuit configured to store the comparison signal outputted from the comparator for each pixel, and generate first and second selection information signals corresponding to the comparison signal; a first buffer configured to buffer the first selection information signal, and generate the compensation control signal; a second buffer configured to buffer the second selection information signal, and generate a selection control signal; and a bias controller configured to generate a bias control signal.

14. The image sensing device of claim 13 , further comprising: a bias current generating circuit configured to supply a bias current, which corresponds to the compensation current, to the compensation circuit based on the bias control signal and the selection control signal.

15. The image sensing device of claim 14 , wherein the bias current generating circuit includes: a current source configured to generate the bias current based on the bias control signal; and a switch configured to selectively couple the current source to the compensation circuit based on the selection control signal.

16. The image sensing device of claim 9 , wherein the pixel is disposed in an analog region, and wherein the compensation control circuit is disposed in a digital region.

17. An operating method of an image sensing device, comprising: determining, during a first frame period, whether at least one depth sensing pixel is saturated, based on a pixel signal read out from the depth sensing pixel; storing, during the first frame period, compensation information of the depth sensing pixel determined to be saturated; and removing, during a second frame period after the first frame period, background light from the depth sensing pixel by supplying a compensation current, which corresponds to the background light, to a floating diffusion node in the depth sensing pixel based on the compensation information.

18. The operating method of claim 17 , wherein the determining includes: converting the pixel signal, as an analog signal, into a digital pixel signal; comparing the digital pixel signal with a reference signal; and determining whether the depth sensing pixel is saturated, according to the comparison result.